Staff Sgt. Mathew R. Marsh, Gunnery Sgt. Gregory J. Mullins, Sgt. Miguel Ortiz and Staff Sgt. Eric W. Summers died after the explosion at Zulu impact area at about 11 a.m. Wednesday. The Marines were disposing of unexploded ordnance at the range, and there was no live-fire training going on in that impact area at the time, base officials said.

A Navy corpsman and two other Marines who were standing nearby during the explosion received medical treatment at the scene, Marines said.

Marsh, 28, of Long Beach, Calif., was assigned to Headquarters and Headquarters Squadron, Marine Corps Air Station Camp Pendleton. He joined the Marine Corps in July 2003 and was promoted to staff sergeant in May 2009.

Marsh’s awards include the Navy and Marine Corps Achievement Medal, Combat Action Ribbon, three Marine Corps Good Conduct Medals, the Afghanistan Campaign Medal, Iraq Campaign Medal and NATO Medal-ISAF Afghanistan. He deployed to Iraq in 2005 and 2008 and to Afghanistan in 2010 and 2012 as a team leader.

Mullins, 31, of Bayou L’Ourse, La., was the explosive ordnance disposal staff noncommissioned officer-in-charge assigned to Headquarters and Headquarters Squadron, Marine Corps Air Station Camp Pendleton. He joined the Marine Corps in March 2002 and was promoted to gunnery sergeant in February 2013.

Mullins’ awards include two Navy and Marine Corps Commendation Medals, Combat Action Ribbon, three Marine Corps Good Conduct Medals, Afghanistan Campaign Medal and NATO Medal-ISAF Afghanistan. He deployed to Afghanistan in 2011 and 2012 as a team leader.

Ortiz, 27, of Vista, Calif., also was assigned to Headquarters and Headquarters Squadron, Marine Corps Air Station Camp Pendleton. He joined the Marine Corps in March 2006 and was promoted to sergeant in November 2009.

Ortiz’s awards include the Navy and Marine Corps Achievement Medal, Combat Action Ribbon, two Marine Corps Good Conduct Medals, Afghanistan Campaign Medal, Iraq Campaign Medal, Korean Defense Service Medal and the NATO Medal-ISAF Afghanistan. He deployed to Iraq in 2007, to the Western Pacific in 2008 and to Afghanistan in 2012.

Summers, 32, of Poplar Bluff, Mo., was assigned to the Explosive Ordnance Disposal Platoon, Airfield Operations Company, Marine Wing Support Squadron 372, Marine Aircraft Group 39. He joined the Marine Corps in July 2000 and was promoted to staff sergeant in October. 2010.

“Today, our thoughts and prayers are with the families of the Marines we lost yesterday,” said Brig. Gen. John W. Bullard, commander of Marine Corps Installations West-Marine Corps Base Camp Pendleton.

“Explosive ordnance disposal is a small and tight-knit community, not just in the Marine Corps, but in the entire U.S. military. Our focus now is on ensuring these families receive the help and support they need,” he said.

The impact area where the Marines were killed is used for firing grenades, mortars, artillery and rockets and for dropping munitions from aircraft. Live-fire training was going on at an adjacent impact area at the time of the explosion, officials said.